1. Field of the Invention
The present invention relates to a thread cutter for a sewing machine, and more specifically, it relates to a thread cutter which is suitably applied to an overlock sewing machine.
2. Description of the Background Art
In order to start a sewing operation with a sewing machine, a needle thread, a looper thread or a bobbin thread is set on a thread guide, and thereafter the free edge of the thread extending from a thread loop catcher such as a needle, a looper or a shuttle is cut into a proper length if the same is too long. Thus, the free edge of the thread is prevented from being stitched into the seam and deteriorating the appearance of the sewn product.
An overlock sewing machine comprises cutters which consist of an upper and a lower knife blade for trimming a cloth edge. These cutters are also adapted to cut a thread extending from a needle or a looper, or a chain loop which is formed following the end of the seam. However, the presser foot of the sewing machine inhibits the needle thread or the looper thread from being brought into the cutters. In particular, the chain loop which is discharged from a rear part of the presser foot must be extremely detoured to the cutters along the presser foot. Further, it is difficult to drive the cutters for cutting the thread or the chain loop, due to co-movement of the needle and the looper.
A thread cutting blade which is embedded in a rear part of a presser foot or a knee lifter lifting lever for cutting a thread is also known in the art. In this case, however, the thread cutting blade is in a fixed state, and hence the thread must be held with both hands and strained to be smoothly cut with the blade. Thus, a plurality of threads or chain loops cannot be readily cut in a single operation. On the other hand, a slit which is provided in a proper portion of a presser bar for serving as a thread cutter is also known in the art. Also in this case, however, the thread must be held with both hands and strained, to be pushed into the slit and cut along an edge of the slit. Thus, the thread cannot be readily cut, and it is further difficult to cut a plurality of threads or chain loops.